Precipitation

• 1). Mix the black liquor with the sulfuric acid. Test the solution for pH (acidity) levels of 2, 4 and 6 during acid addition and separate the solution into three batches. Wait for lignin to precipitate from each of the three solutions.
  
  
• 2). Set up the Bukner flask, filter and filter paper. Filter each precipitate from the acid solution. Wash the precipitates with water until they reaches a neutral pH of close to 7 at 77 degree Fahrenheit. Dry the lignin residue in an oven for 24 hours at 131 degrees Fahrenheit.
  
  
• 3). Choose the pH 4 lignin precipitate and mix it with dichloromethane in a ratio of 1 to 10 based on weight. Stir vigorously for one hour at room temperature. Filter, keeping the solution and discarding the undissolved solid.
  
  
• 4). Make a caustic soda solution by dissolving caustic soda crystals in water with a weight based ratio of one part caustic soda crystals to two parts water. Dissolve equal weights of wheat straw for a filler and wheat flour for the extender with the 50 percent caustic soda solution. Add the same weight of lignin solution to complete the adhesive mixture.
  
  
• 5). Cure the adhesive solution in an oven at 266 to 300 degrees Fahrenheit for eight hours. Allow cooling and the glue is ready.